In present day canning factories, conveyer speeds in excess of one thousand units per minute are not unusual. Not only do the high operating speeds cause occasional damage to the containers as they move along the conveyer, but the high speed also makes inspection for any damaged units extremely difficult. In U.S. Pat. No. 3,131,815, issued May 5, 1964 to B. B. Mathias, method and apparatus are disclosed for inspecting sealed containers by detecting a light beam reflected from a surface of the container. If the surface under inspection is of a predetermined configuration, the reflected light is focused upon a first detector. Should the surface be deformed, some light will be reflected through one or more laterally located lenses to impinge upon a second detector. Energization of the second detector generates a signal to identify the defective container. William T. Plummer et al., in U.S. Pat. No. 3,761,179, issued Sept. 25, 1973, discloses apparatus for testing a mirrored surface by detecting the light reflected from the surface. Inspections which rely on reflected light are adversely affected by the presence of dirt, foreign matter or overflow from the containers. Because foreign material cannot be completely avoided in a canning factory, inspection systems of the Plummer type will unnecessarily reject a container merely because the inspected surface is dirty; similarly, diffused surfaces will generate error signals falsely indicative of damaged or deformed containers.
It is therefore an object of our invention to inspect containers without regard to the specular reflective characteristics of the tested containers.
The testing disclosed by the Mathias apparatus is effective only after a container has been filled and sealed since the presence of a vacuum within the container is required. No provision is made for detecting defective containers prior to the filling and sealing operations. As a result, every container, whether defective or not, must be filled and sealed prior to being inspected. Any material used to fill a defective container is wasted. If defective containers were identified prior to the filling and sealing operation, contents could be saved that would otherwise be wasted by filling defective containers.
It is therefore also an object of our invention to inspect containers prior to the filling thereof to determine the presence of defects in the containers.
The patent to Shibata et al., U.S. Pat. No. 3,794,427, issued Feb. 26, 1974, describes apparatus which employs the principles of light reflection (angle of incidence equals angle of reflection) to detect conformity of a surface under inspection with a predetermined norm. A television camera scans or views the reflection received from an illuminated object traveling in a direction transverse to the source of light. The amplitude of the signal generated by the television camera during the scan is correlated with respect to a time base and compared with the amplitude per time base of a norm. An output signal responsive to the comparison step is generated to provide an indication of conformity with the norm of the object under inspection.
Another object of the present invention is to provide an inspection system wherein the detector system does not scan the surface under inspection.
Still another object of the present invention is to provide an inspection system wherein a light source and light detection system are not necessarily transverse to and at opposed sides of the object under inspection.
Dimensional inspection of objects can be accomplished optically. In U.S. Pat. No. 3,536,405, issued Oct. 27, 1970, to R. A. Flower, a system for inspecting the thickness of a sample is disclosed. Similarly, L. F. Flaczynski in U.S. Pat. No. 3,682,554, issued Aug. 8, 1974, discloses a method and apparatus for dimensionally inspecting conveyer goods while they move along the conveyer. The patent to Hietanen et al., U.S. Pat. No. 3,749,496, issued July 31, 1973, describes an inspection system employing a laser. The intensity of the lased surface, on comparison with a norm, provides an indication of the degree of conformity of the object under inspection. Size gauging method and apparatus are disclosed in U.S. Pat. No. 3,791,741, issued Feb. 12, 1974, to I. R. Brenholdt. Each of the above cited references is capable of optically inspecting a sample to determine its dimensional characteristics within a given tolerance. However, the apparatus disclosed in each of the references would be unable to detect a defect in a container shape unless that defect appeared in the specific surface being inspected and affected its size. For example, a can which had a hole in the middle of the inspected surface could pass a height and width dimensional inspection because the hole would not alter the external dimensions of the surface. However, such a defective can should be detected by a sophisticated inspection system to prevent a wasteful filling operation.
It is another object of our invention to inspect container goods simultaneously for dimensional variation and non-dimensional defects.
R. A. Webster in U.S. Pat. No. 3,222,979, issued Dec. 14, 1965, discloses an electron-optics device for dimensionally inspecting objects. The device employs a scanning electron beam to inspect the object. The electron scan is converted into a video output for determing the acceptability of the inspected object. The scanning beam is a movable source, returning periodically to some starting point for initiating the scan of a subsequent object. Because of the time required to scan a sample, such device could not be effectively employed in a conveyer system operating at the speeds previously indicated.
It is yet another object of our invention to employ a fixed position beam to inspect containers.
U.S. Pat. No. 3,619,578 which issued Sept. 22, 1969, to P. George and U.S. Pat. No. 3,695,771, which issued Oct. 3, 1972 to A. M. Bardos, disclose inspection equipment for detecting surface irregularities on inspected samples. Both disclosed patents are limited to determining defects in surface smoothness.
It is one of the objects of our invention to simultaneously inspect a container for dimensional conformity and surface acceptability.
All the inspection systems discussed above have been effective for inspecting a single surface of a sample. However, a container may have defects on any of its surfaces which require rejection of the container. Because the above systems cannot interpret the effect a defect in one surface has on other surfaces of a container, defects on surfaces other than the inspected surface would not be detected.
It is still another object of our invention to permit simultaneous testing of any or all surfaces of a container for the presence of defects.
An additional object of our invention is to permit the detection of defects in any surface of a container by inspecting a portion of a single surface of the container.
A further object of the present invention is to employ a gating system for initiating and terminating the inspection process.
A still further object of the present invention is to correlate the translational position of the object under inspection with the simultaneous information acquired by the inspection system.
A yet further object of the present invention is to gate an inspection system independent of the translational speed of the object under inspection.